Method for assaying arylsulfatase activity

ABSTRACT

A lactase preparation includes lactase and has a lactase activity of 4,000 NLU/g or more according to the FCC IV method, wherein the lactase originates from a lactase gene of yeast, and wherein the lactase preparation has an arylsulfatase activity of 0.1% or less based on the lactase activity, in which the arylsulfatase activity (unit: U/g) is determined and calculated.

TECHNICAL FIELD

The present invention relates to a high sensitive method for determiningactivity of arylsulfatase, a lactase preparation in which it has beenconfirmed that arylsulfatase does not contaminate the preparation orexists in a small amount if it contaminates the preparation by the highsensitive method of arylsulfatase according to the present invention, amethod for producing such a lactase preparation, and a dairy productthat has been produced by using such a lactase preparation.

BACKGROUND ART

Since ancient times, cow milk has been applied as a nutritious anduseful food over the long term. Cow milk comprises lactose that is oneof sugar. The lactose is decomposed by lactase in intestine. However,because in part of humans secretion volume of lactase into intestinedecreases with growth, the part of humans develop so-called lactoseintolerance with symptoms of abdominal pain and diarrhea if they takes alarge amount of cow milk or its processed product (hereaftercollectively-referred to “a dairy product”). This has been one reason bywhich a wide intake of this nutritious food is prohibited.

In recent years, dairy products from which lactose is previously reducedor removed are provided. The humans suffering from lactose intolerancecan also intake such a dairy product without any problems.

The reduction or removal of lactose is performed by various methods, andthe most common method is one in which lactose is hydrolyzed by treatinga dairy product with a lactase preparation.

Previously, dairy products that had been obtained by decomposing lactosewith lactase were commonly distributed after a sterilization step.However, recently, a means is prevalent, in which means a lactasepreparation is added to sterile cow milk under aseptic conditions andlactose is decomposed during distribution. There are thought that bythis means the amount of the lactase preparation to be used can bereduced and that this means contributes to cost reduction.

On the other hand, by employing the means in which a lactase preparationis added to sterile cow milk under aseptic conditions, a new problem hasbeen arisen. It is a problem, of which cause is that contaminatedenzymes (protease and arylsulfatase) that are contained in a smallamount in the lactase preparation cause changes to milk constituentsbecause those enzymes have not been inactivated. In fact, it has beenknown that protease causes curd or development of bitter taste. Further,in Non-patent Literature 1, it is reported that arylsulfatase causesdevelopments of unreasonable and undesirable taste and smell.

Patent Literature 1 describes a lactase preparation in which the amountof contaminated arylsulfatase is reduced and a method for producing it.However, by the method for determining activity of arylsulfatase that isdescribed in Patent Literature 1, arylsulfatase activity cannot bedetermined in a range of trace amounts of 8 units or less (arylsulfataseactivity per 1 NLU of a substance having lactase activity, hereafter thesame shall be applied), and it is only described as a detection limit orless. Further, Table 1 of Patent Literature 1 describes that if theactivity of the contaminated arylsulfatase is 19 units or less,off-flavor will not occur in the dairy product. However, this judgmentis based on the result of a short-term examination in which the reactionterm is 2 days. It is inferred that the cause, by which off-flavordevelops in dairy products, is a chemical change of a milk constituentby an enzyme, arylsulfatase, and a long reaction term of 2 to 3 monthsor more is assumed in shelf-stable milk at ordinary temperatures (UHTmilk) as its use. If so, it cannot be said that a lactase preparationhaving an arylsulfatase activity of 19 units or less, which has beendetermined by the method according to Patent Literature 1, will notdevelop off-flavor in dairy products. They go without saying that it isnecessary to control more rigorously the amount of the contaminatedarylsulfatase and that it is necessary to employ a higher sensitivemethod for determining activity of arylsulfatase to control the amountof the contaminated arylsulfatase.

To eliminate the arylsulfatase that contaminates an enzyme preparationto be the minimum quantity, we should perform purification by combininggeneral purification methods. Alternatively, we should select amicrooraganism that can produce an intended enzyme, of whicharylsulfatase producibility has been deleted, and culture themicrooraganism. Also, we can use a microorganism which has been obtainedby transforming a host that intrinsically produces no arylsulfatase tohave it producing an intended enzyme.

Patent Literature 1 includes descriptions about a process for obtaininga microorganism, of which arylsulfatase producibility has been reducedby mutation treatments, and a microorganism, of which arylsulfatase genehas been deleted by genetic engineering procedures. However, althoughthe process for obtaining a microorganism, of which arylsulfataseproducibility has been reduced by mutation treatments, is described,there is no example in which the microorganism has been actuallyobtained. Namely, only a possibility for it is shown. In other words, itis unexplained whether the microorganism, of which arylsulfataseproducibility has been reduced by mutation treatments, can be producedin an industrial scale according to the process as described in PatentLiterature 1. To disrupt arylsulfatase genes by mutation in a diploidstrain of yeast that is useful for producing a lactase preparation in anindustrial scale, it is necessary to obtain a double mutant. Theobtaining of such a double mutant has been thought to be difficult inpractice.

About the deletion of the arylsulfatase gene by genetic engineeringprocedures, only an example of CBS2359 strain that is a monoploid isdescribed in Patent Literature 1. In other words, by the process asdescribed in Patent Literature 1, it is difficult to effectively disruptgenes in a diploid strain of yeast that is useful for producing alactase preparation, and thus a strain that does not producearylsulfatase and that is a diploid strain of yeast cannot be prepared.

About the lactase activity of the lactase preparations that aredescribed in examples of Patent Literature 1, it is about 5,000 to 5,500NLU/g for Maxilact (registered trademark) LG5000 (produced by DSM) andabout 5,000 to 5,500 NLU/g for GODO YNL2 (produced by Godo Shusei Co.,Ltd.). Further, the lactase activity of the lactase preparation isunclear, of which preparation has been produced from lactase that hasbeen produced by a microorganism, of which arylsulfatase producibilityhas been reduced by the mutation treatments that are described inexamples of Patent Literature 1. However, if the amount of the lactasepreparation that is added to a dairy product is increased to obtain asufficient lactase activity, as a matter of course, the absolute amountof arylsulfatase that contaminates the lactase preparation willincrease. Therefore, the potential of development of off-flavor will beenhanced in dairy products such as shelf-stable milk at ordinarytemperatures (UHT milk).

PRIOR-ART LITERATURES Patent Literatures

Patent Literature 1: Japanese Patent Laid-open No. 2009-517061

Non-Patent Literatures

Non-patent Literature 1: V Lopez, R. C., J. Agric. Food Chem. (1993),41, p.p. 446-454

SUMMARY OF INVENTION Problems to be Solved by Invention

Even if the amount of arylsulfatase that contaminates a lactasepreparation is a tiny amount, depending on the term of action, atemperature condition, or the like unreasonable and undesirable tasteand smell can be developed when the lactase preparation is used byadding it to milk or a dairy product. Not to cause such a disadvantage,a lactase preparation having a higher lactase activity is desired, inwhich preparation the amount of arylsulfatase contaminated is reduced tobe a minimum quantity, and preferably the arylsulfatase is completelyeliminated. For this purpose, it is necessary to develop a method fordetermining activity of arylsulfatase, by which method, it can beconfirmed that the amount of the arylsulfatase contaminated in thelactase preparation is reduced to be a minimum quantity.

Means for Solving Problem

The present inventors have extensively studied to solve the aboveproblem and have developed a method for determining activity ofarylsulfatase in an aqueous system having a sensitivity higher than thatof a conventional method. Further, by the method for determiningactivity of arylsulfatase having a sensitivity higher than that of theconventional method, which is a fluorescence one, they have determinedthe activity of arylsulfatase that has contaminated a lactasepreparation in a region where it has conventionally considered as to beequal to or less than the detection limit, and have specified thecontaminated amount of the arylsulfatase, at which amount it will notdevelop undesirable taste or smell in milk or dairy products. Thus, theyhave accomplished the present invention.

Namely, the present invention relates to a method for determiningactivity of arylsulfatase in an aqueous system characterized in thatarylsulfatase is subjected to reaction with a substrate, from whichfluorophore or chromophore is liberated by suffering an action of thearylsulfatase, in an aqueous reaction system having high ionic strength.

Preferable examples of means for reaction in an aqueous reaction systemhaving high ionic strength are one in which the enzyme is subjected toreaction with a substrate in an aqueous reaction system to which aninorganic salt has been added, and/or, another one in which the enzymeis subjected to reaction with a substrate in a buffer that does notdenature the enzyme protein.

The preferable range of the concentration of the inorganic salt in theaqueous reaction system is 10 to 1000 mM and more preferable range of itis 50 to 500 mM, and the preferable range of the concentration of thebuffer is 10 to 200 mM and more preferable range of it is 50 to 200 mM.

The above inorganic salt is preferably at least one member selected fromthe group consisting of potassium chloride, sodium chloride, andammonium sulfate. Also, the above buffer is preferably a phosphatebuffer.

The above method for determining activity of arylsulfatase in an aqueoussystem according to the present invention is particularly preferably onecomprising the following steps (1) to (10):

-   (1) A specimen in which the existence of the arylsulfatase is    predicted is arbitrarily diluted with 100 mM potassium phosphate    buffer (pH6.5) comprising 0.5M potassium chloride to obtain a    sample.-   (2) An aqueous solution comprising potassium 4-methylumbelliferone    sulfate in a concentration of 2 mM is prepared.-   (3) The sample and the aqueous potassium 4-methylumbelliferone    sulfate solution are mixed with each other at a ratio of 1:1 (volume    basis) and are reacted at 37 degrees Celsius for 3 hours.-   (4) To the reacted solution, 0.1N aqueous sodium hydroxide solution    having the same amount (volume basis) as that of the reacted    solution is added to stop the reaction, thus obtaining a sample for    determination.-   (5) Fluorescence intensity is determined at an excitation wavelength    of 360 nm and a fluorescence wavelength of 450 nm.-   (6) 4-Methylumbelliferone is dissolved in 100 mM potassium phosphate    buffer (pH6.5) comprising 0.5M potassium chloride to obtain a    solution having an appropriate concentration, 0.1N aqueous sodium    hydroxide solution is added in a similar way as that in step (4),    and fluorescence intensity is determined under the same conditions    as those in step (5).-   (7) From step (6), a calibration curve is prepared,-   (8) From the fluorescence intensity that was determined in step (5)    and the calibration curve that was prepared in step (7), the    concentration of 4-methylumbelliferone of the sample for    determination is calculated, and the calculated value is divided by    3, thus obtaining the concentration of the 4-methylumbelliferone in    the case where the reaction time of period is 1 hour. Further, from    the volume of the reacted solution, the amount of the    4-methylumbelliferone that was liberated by the reaction of 1 hour    is calculated.-   (9) Because the amount of the 4-methylumbelliferone thus calculated    is based on the amount of the specimen that was contained in the    sample prepared in step (1), the calculated. amount is converted to    that of the 4-methylumbelliferone per 1 g of the specimen.-   (10) When the amount of the 4-methylumbelliferone that was liberated    per 1 hour of the time of period of the reaction of the substrate    and the enzyme is 1 nmole, it is defined as 1 unit(U), and the unit    is shown as a unit amount per 1 g of the specimen (i.e., an enzyme    preparation), namely, “unit(U)/g”.

In step (10), the “substrate” is potassium 4-methylumbelliferone sulfateand the “enzyme” is arylsulfatase.

The above method for determining activity of arylsulfatase in an aqueoussystem according to the present invention can be applied for determiningactivity of arylsulfatase in a lactase preparation.

Further, the present invention relates to a lactase preparation producedby using, as a raw material, cultured yeast or microorganic cells and/orculture fluid of those cells, wherein the yeast or microorganic cellsare those of a diploid strain of yeast having a lactase gene, in whichexpression of arylsulfatase protein is restricted, or a gene-recombinantmicroorganism in which a lactase gene of yeast has been transformed andexpression of arylsulfatase protein is restricted, characterized in thatthe lactase preparation has a lactase activity of 4,000 NLU/g or moreaccording to the FCC IV method and has an arylsulfatase activity of0.1.% or less of the lactase activity as the basis, in which thearylsulfatase activity (unit: U/g) has been determined and calculated bythe method for determining activity of arylsulfatase in an aqueoussystem according to the present invention comprising the above steps (1)to (10).

The above lactase preparation according to the present invention canalso be prepared without a step for removing arylsulfatase. Here, the“step for removing arylsulfatase” does not include such a step thatarylsulfatase protein is purified with lactase protein as an intendedenzyme, such as, e.g., ammonium sulfate fractionation um an aqueoussolution comprising an intended enzyme, among fractionation andpurification methods that are performed in this technical field. Thestep is one by which the lactase protein as the intended enzyme isseparated from the arylsulfatase protein.

In the above present invention, “expression of arylsulfatase protein isrestricted” means that arylsulfatase protein is not produced or itsproduction amount is reduced bemuse, e.g., an arylsulfatase gene(structural gene) has been disrupted, an expression regulation gene thatworks the arylsulfatase gene to express arylsulfatase protein has beendisrupted, or there is no arylsulfatase gene and/or no expressionregulation gene for the arylsulfatase protein. It is preferable thatthere is no expression of arylsulfatase protein, i.e., its productionamount is zero. However, it is acceptable that the expression of thearylsulfatase proteion is restricted so that the ratio of thearylsulfatase activity (unit: U/g) to the lactase activity (unit: NLU/g)will be 0.1% or less, preferably 0.02% or less.

Further, although the lactase preparation according to the presentinvention has a lactase activity of 4,000 NLU/g or more, it ispreferably 4,500 NLU/g or more, and more preferably 5,000 NLU/g or more.

The diploid strain of yeast having a lactase gene in which expression ofarylsulfatase protein is restricted may be a mutant that has beenobtained by treating a diploid strain of yeast to mutate it or may beanother mutant that has been obtained by manipulating a diploid strainof yeast to delete an arylsulfatase gene or a gene to regulateexpression of an arylsulfatase protein. A mutant is preferable, of whichparent strain is a diploid strain of yeast having a large amount ofproduction of lactase protein.

The diploid strain of yeast is preferably a diploid strain ofKluyveromyces lactis or Kluyveromyces marxianus that is closely relatedto the Kluyveromyces lactis Further, a gene-recombinant microorganism,in which a lactase gene of yeast has been transformed and expression ofarylsulfatase protein is restricted, is preferably a gene-recombinantmicroorganism, to which a lactase gene of Kluyveromyces lactis orKluyveromyces marxianus has been transformed.

The present invention also relates to a method for producing a lactasepreparation characterized by culturing a diploid strain of yeast havinga lactase gene, in which expression of arylsulfatase protein isrestricted, or a gene-recombinant microorganism in which a lactase geneof yeast has been transformed and expression of arylsulfatase protein isrestricted; gathering yeast or microorganic cells without destroyingtheir cell walls, gathering culture fluid with yeast or microorganiccells after destruction of their cell walls, or gathering culture fluidwithout destroying cell walls; and preparing a lactase preparationhaving a lactase activity of 4,000 NLU/g or more according to the FCC IVmethod and. an arylsulfatase activity of 0.1% or less of the lactaseactivity as the basis, in which the arylsulfatase activity (unit: U/g)has been determined and calculated by the method for determiningactivity of arylsulfatase in an aqueous system according to the presentinvention comprising above steps (1) to (10), by using, as a rawmaterial, the gathered yeast or microorganic cells and/or gatheredculture fluid without a step for removing arylsulfatase. The case whereculture fluid is gathered without destroying cell walls is such a casethat the gene-recombinant microorganism secretes lactase.

The steps for preparing lactase preparation can comprise purificationsteps that are performed in this technical field, such as concentrationof lactase protein. However, in the method for producing a lactasepreparation according to the present invention, a step for removingarylsulfatase is not performed. Because a diploid strain of yeast or agene-recombinant microorganism is used, in which it produces lactaseprotein having high activity and the production amount of arylsulfataseprotein contaminated is very small even if it exists, a lactasepreparation having high lactase activity can be obtained even though theconcentration rate of the produced lactase protein is not large, andbecause the concentration rate is not large, the arylsulfatase proteincontaminated does not become high activity even if it has beenconcentrated.

Furthermore, the present invention relates to a dairy product that hasbeen produced by using the lactase preparation according to the presentinvention.

Effects of Invention

In the method for determining activity of arylsulfatase in an aqueoussystem according to the present invention, arylsulfatase of much lessamount than that of before can be determined by using its activity as anindicator. Because a high sensitive method for determining activity ofarylsulfatase was established according to the present invention, it hasbecome possible to exactly know the amount of arylsulfatase in a lactasepreparation by using its activity as an indicator.

Also, it has become possible to provide a lactase preparation havinghigh lactase activity and having a very small amount of arylsulfatasecontaminated or no arylsulfatase by using, as a raw material, culturedyeast or microorganic cells and/or culture fluid of those cells, whereinthe yeast or microorganic cells are those of a diploid strain of yeasthaving a lactase gene in which expression of arylsulfatase protein isrestricted or those of a gene-recombinant microorganism in which alactase gene of yeast has been transformed and expression ofarylsulfatase protein is restricted. Because the lactase preparation ofthe present invention has high lactase activity; an effect can beattained, of which effect is that the usage of the preparation can bereduced, and thus another effect can also be attained, of which effectis that amounts of additives such as stabilizers or impurities that areintroduced to the objective, to which e preparation is added, can bereduced even if the preparation contains the additives or theimpurities.

When a diploid strain of yeast is used, there are such advantages thatits property is more difficultly altered than that of a monoploid straineven after continuation of subculture, and that the production amount ofa protein per a unit amount of culture fluid is generally larger thanthat of a monoploid strain.

When the lactase preparation of the present invention is used, such aneffect can be attained that the development of unreasonable andundesirable taste and smell can be suppressed in shelf-stable milk atordinary temperatures (UHT milk) or the like.

According to the method for producing a lactase preparation of thepresent invention, a lactase preparation having high lactase activity isproduced without a step for removing arylsulfatase contaminated. Becausethis method does not comprise “the step for removing arylsulfatase,” itsproduction efficiency is high and there is no reduction of lactaseactivity in purification steps for removing arylsulfatase.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 It is a graph that shows a result of determination ofarylsulfatase activity by a colorimetric method.

FIG. 2 It is a graph that shows a result of determination ofarylsulfatase activity by a fluorescence method.

FIG. 3 It is a schematic diagram that shows a method for constructing avector pdSuC1 for disrupting arylsulfatase gene.

FIG. 4 It is a schematic diagram that shows a method for constructing avector pdSuCM6 for disrupting arylsulfatase gene.

FIG. 5 It is a schematic diagram that shows a method for introducing twovectors for disrupting arylsulfatase genes.

FIG. 6 It is a photograph that shows results of Southern blottings of astrain comprising two arylsulfatase genes, another strain in which onearylsulfatase gene has been disrupted, and the other strain in which twoarylsulfatase genes have been disrupted.

EMBODIMENTS FOR PERFORMING INVENTION

First, a method for determining activity of arylsulfatase will beexplained.

The method that has been conventionally known as a method fordetermining activity of arylsulfatase is a calorimetric one, in which acompound comprising a chromophore such as p-nitrophenol and a sulfategroup that is coupled to the chromophore is used as a substrate. In thismethod, the amount of the chromophore is determined by absorbance, inwhich the chromophore has been liberated because the sulfate group hasleft from the substrate by a reaction of the substrate witharylsulfatase. However, when the amount of the liberated chromophoresuch as p-nitrophenol is low, the change of the absorbance is small andthus it is difficult to obtain a clear determination value.

As a method for determining activity of arylsulfatase, a fluorescencemethod has also been known (Method in Enzymology 11/21), in which acompound comprising a fluorophore and a sulfate group that is coupled tothe fluorophore, e.g., 4-methylumbelliferone sulfate, is used as asubstrate. It is said that the sensitivity of a fluorescence method isgenerally at least hundred times that of a calorimetric one.

The present inventors have studied the conditions for determination,under which conditions a sensitivity higher than that of a conventionalcalorimetric or fluorescence method can be attained in a method fordetermining activity of arylsulfatase in an aqueous system. They havearrived at a version that the arylsulfatase activity can be determinedwith a high sensitivity by increasing ionic strength in a reactionsystem of an enzyme with a substrate. Thus, they have established themethod for determining activity of arylsulfatase according to thepresent invention. It has been absolutely unknown in the past that byincreasing ionic strength in an aqueous reaction system whenarylsulfatase is reacted with its substrate, the enzyme reaction isremarkably activated and as a result a chromophore or fluorophore isliberated in a more amount. By performing the method for determiningactivity of arylsulfatase in an aqueous system according to the presentinvention in a fluorescence method, it has become possible to exactlyknow the amount of arylsulfatase contaminated in a lactase preparation.As a result, it has become possible to provide a lactase preparation, ofwhich arylsulfatase amount is zero or a very, very small.

The method for determining activity of arylsulfatase in an aqueoussystem according to the present invention is characterized in that whenarylsulfatase is reacted with its substrate (with the proviso that thesubstrate liberates fluorophore or chromophore by suffering an action ofthe arylsulfatase), ionic strength of the reaction system is increased.Specific means for increasing the ionic strength in the reaction systeminclude one wherein an inorganic salt is coexisted and another onewherein the enzyme reaction is performed in a buffer system.

Examples of inorganic salts that should be added to the reaction systeminclude potassium chloride, sodium chloride, ammonium sulfate, and thelike. The concentration of such an inorganic salt is, for example, 10 to1000 mM, and preferably 50 to 500 mM in the reaction system. Examples ofbuffer include phosphate buffers such as phosphoric acid-potassiumphosphate buffers (wherein the concept of potassium phosphate includespotassium dihydroxyphosphate, dipotassium hydroxyphosphate, andtripotassium phosphate), phosphoric acid-sodium phosphate buffers(wherein the concept of sodium phosphate includes sodiumdihydroxy-phosphate, disodium hydroxyphosphate, and trisodiumphosphate), and phosphate buffered saline, which do not denature anenzyme protein. The concentration of the buffer in the reaction systemis, for example, 10 to 200 mM, and preferably 50 to 200 mM. To coexistthe inorganic salt in the reaction system, for example, an inorganicsalt may be added to an aqueous solution of a specimen in which theexistence of arylsulfatase is predicted (for example, one obtained bydissolving the specimen in water or a buffer), or an inorganic salt maybe added to an aqueous solution of a substrate.

A typical example of the method for determining activity ofarylsulfatase in an aqueous system according to the present invention isas follows:

-   (1) A specimen in which the existence of arylsulfatase is predicted    is arbitrarily diluted with 100 mM potassium phosphate buffer    (pH6.5) comprising 0.5M potassium chloride to obtain a sample.-   (2) An aqueous solution comprising potassium 4-methylumbelliferone    sulfate in a concentration of 2 mM is prepared.-   (3) The sample and the aqueous potassium 4-methylumbelliferone    sulfate solution are mixed with each other at a ratio of 1:1 (volume    basis) and are reacted at 37 degrees Celsius for 3 hours.-   (4) To the reacted solution, 0.1N aqueous sodium hydroxide solution    having the same amount (volume basis) as that of the reacted    solution is added to stop the reaction, thus obtaining a sample for    determination.-   (5) Fluorescence intensity is determined at an excitation wavelength    of 360 nm and a fluorescence wavelength of 450 nm.-   (6) 4-Methylumbelliferone is dissolved in 100 mM potassium phosphate    buffer (pH6.5) comprising 0.5M potassium chloride to obtain a    solution having an appropriate concentration, 0.1N aqueous sodium    hydroxide solution is added in a similar way as that in step (4),    and fluorescence intensity is determined under the same conditions    as those in step (5).-   (7) From step (6), a calibration curve is prepared.-   (8) From the fluorescence intensity that was determined in step (5)    and the calibration curve that was prepared in step (7), the    concentration of 4-methylumbelliferone of the sample for    determination is calculated, and the calculated value is divided by    3, thus obtaining the concentration of the 4-methylumbelliferone in    the case where the reaction time of period is 1 hour. Further, from    the volume of the reacted solution, the amount of the    4-methylumbelliferone that was liberated by the reaction of 1 hour    is calculated.-   (9) Because the amount of the 4-methylumbelliferone thus calculated    is based on the amount of the specimen that was contained in the    sample prepared in step (1), the calculated amount is converted to    that of the 4-methylumbelliferone per 1 g of the specimen.-   (10) When the amount of the 4-methylumbelliferone that was liberated    per 1 hour of the time of period of the reaction of the substrate    and the enzyme is 1nmole, it is defined as 1 unit(U), and the unit    is shown as a unit amount per 1 g of the specimen (i.e., an enzyme    preparation), namely, “unit(U)/g”.

The lactase preparation according to the present invention has a lactaseactivity of 4,000 NLU/g or more (preferably 4,500 NLU/g or more, stillmore preferably 5,000 NLU/g or more) according to the FCC IV method(Food Chemicals Codex Fourth Edition, effective Jul. 1, 1996, Committeeon Food Chemicals odex p.p. 801-802), and an arylsulfatase activity of0.1% or less (preferably 0.02% or less) of the lactase activity (unit:NLU/g) of the FCC IV method as the basis, in which the arylsulfataseactivity is determined and calculated by the method that is describedabove as a specific example of the method for determining activity ofarylsulfatase according to the present invention.

In the production of the lactase preparation according to the presentinvention, a diploid strain of yeast having a lactase gene is used, inwhich strain expression of arylsulfatase protein is restricted and bywhich strain lactase protein is produced. Further, the diploid strain ofyeast that is used in the present invention is one that produces lactaseprotein with a high activity, which can provide a lactase preparation of4,000 NLU/g or more as it is or by concentrating it. The diploid strainof yeast is, for example, a mutant that can be obtained by treating amicroorganism to mutate it. Such a mutant can be obtained by, forexample, a method wherein a diploid strain of yeast that produceslactase protein with high activity is exposed to ultraviolet irradiationor a chemical mutagen to perform mutation, thus disrupting or deletingarylsulfatase genes or genes to regulate expression of arylsulfataseprotein about both genes of the diploid, or a method whereinarylsulfatase genes or genes to regulate expression of arylsulfataseprotein are deleted by genetic engineering procedures about both genesof the diploid. To know whether a desired mutant can be obtained,arylsulfatase activity of a culture fluid in which the mutated yeast hasbeen cultured should be determined by the method (fluorescence method)for determining activity of arylsulfatase according to the presentinvention

Mutation induction by ultraviolet is performed by, for example,irradiating ultraviolet to a suspension of a diploid yeast. Chemicalmutagenesis is performed by, for example, adding a chemical mutagen to asuspension of a diploid yeast. Examples of the chemical mutagen include5-bromouracil, 2-aminopurine, nitrous acid, hydroxyl-amine, acriflavine,methanesulfonate compounds, nitrosoguanidine, and the like.

To delete arylsulfatase genes or genes to regulate expression of anarylsulfatase protein by genetic engineering procedures, common geneticengineering procedures should be applied, for example, obtaining a genefragment having a sequence that is homologous to the sequence of thegene that is intended to be deleted, sub-cloning the fragment to avector to construct a new vector for disrupting the gene that isintended to be deleted, and transforming a diploid strain of yeast byusing the new vector.

In the production of the lactase preparation according to the presentinvention, a gene-recombinant microorganism that produces lactaseprotein with high activity can also be used, in which a lactase gene ofyeast has been transformed so that lactase protein is expressed andexpression of arylsulfatase protein is restricted. As described before,“expression of arylsulfatase protein is restricted” means thatarylsulfatase protein is not produced or its production amount isreduced, because, for example, genes that relate to the production ofarylsulfatase protein are restricted, specifically because there are noarylsulfatase gene and/or no gene to regulate expression ofarylsulfatase protein, or, because an arylsulfatase gene (structuregene) has been disrupted or an expression regulating gene thatencourages arylsulfatage gene to express arylsulfatase protein has beendisrupted.

The gene-recombinant microorganism in which a lactose gene of yeast hasbeen transformed and expression of arylsulfatase protein is restrictedcan be produced by a known method. For example, to a plasmid that istolerant to medicine A, a lactase gene is inserted, with a gene toregulate expression of lactase gene if necessary By using the plasmid toexpress lactase thus prepared, a microorganism as a host is transformed.The microorganism that has been transformed is cultured in a mediumcomprising medicine A, and appeared colonies are selected.

As the host to obtain the gene-recombinant microorganism in whichlactase gene of yeast has been transformed and expression ofarylsulfatase protein is restricted, Escherichia coli, yeast, Bacillussubtilis, and the like can be used.

AS the host to obtain the gene-recombinant microorganism in whichlactase gene of yeast has been transformed and expression ofarylsulfatase protein is restricted, it is preferable to use a hostintrinsically having no arylsulfatase gene nor a gene to regulateexpression of arylsulfatase protein, or another host of whicharylsulfatase gene or a gene to regulate expression of arylsulfataseprotein has been disrupted or deleted.

The lactase for the lactase preparation is produced by culturing adiploid strain of yeast having a lactase gene in which expression ofarylsulfatase protein is restricted or a gene-recombinant microorganismin which a lactase gene of yeast has been transformed and expression ofarylsulfatase protein is restricted, wherein the diploid strain of yeastand the microorganism produce lactase protein having high activity;gathering the yeast or microorganic cells without destroying their cellwalls, gathering culture fluid with yeast or microorganic cells afterdestruction of their cell walls, or gathering culture fluid withoutdestroying cell walls; and using as a raw material the gathered yeast ormicroorganic cells and/or the culture fluid, without any step forremoving arylsulfatase. The concept of “culture fluid” includes also aculture supernatant.

To culture microorganism such as yeast, an incubator such as a flask, ajar, and a tank can be used. As the culturing conditions, temperature,pH, a stirring number, and the like, which are suitable for an enzymeproduction by the microoraganism, are selected.

After the completion of culture, a culture fluid comprising lactasedissolved is obtained by generally destroying cell walls. In the casewhere the microorganism that has been cultured secretes lactase, it maybe unnecessary to destroy the cell walls. In the case where a culturefluid is not used and only yeast cells (or microorganic cells) have beengathered, then cell walls of the yeast cells (or microorganic cells) aredestroyed in distilled water, and constituents contained in the cellsare dissolved in the distilled water to be an aqueous solutioncomprising the yeast cells (or microorganic cells).

The culture fluid or the aqueous solution comprising or not comprisingthe yeast or microorganic cells is generally divided into supernatantand residues by an appropriate method such as centrifugation,filtration, or the like, which is commonly performed in this technicalfield. The supernatant may be used as an enzyme fluid as it is. Or afterits concentration is increased by using ultrafiltration membrane or thelike, the concentrated one may be used as an enzyme fluid. The enzymefluid may be pulverized by a method such as spray dry, freeze dry or thelike. The enzyme fluid itself can also be used as a lactase preparation.

The lactase preparation according to the present invention is producedby using a diploid strain of yeast or a microorganism that produceslactase protein having high activity and does not produce arylsulfataseprotein or produces it only infinitesimal quantity Therefore, generallyit is unnecessary to do, for removing arylsulfatase only, one or moreoperations among purification operations such as adsorption,chromatography, crystallization, and the like by using the culture fluidor the like. The method for producing a lactase preparation according tothe present invention does not include any step for removingarylsulfatase. As described before, purification methods by whichlactase protein is not separated from arylsulfatase protein, such assolvent fractionation, ammonium sulfate fractionation, and the like, arenot included within the definition of “a step for removingarylsulfatase.”

An essential constituent of the lactase preparation according to thepresent invention is lactase. In the lactase preparation, any otherconstituent may exist, as long as the substance does not inhibit theactivity of lactase and its amount is one by which the activity oflactase is not inhibited; or as long as the substance does notundesirably interact with an objective for which the lactase preparationis used. Examples of the substance that may exist include those thatcontribute stabilization of lactase, such as metallic salts, varioussugars, ascorbic acid, glycerol, and the like, excipients that are usedto increase usability such as starches and dextrin, and inorganic saltsand the like that have buffering action. The state of the lactasepreparation is not particularly restricted. Its state may be, forexample, powder, granule, solution, or the like.

The present invention also relates to dairy products that have beenproduced by using the lactase preparation according to the presentinvention. The dairy products include milks such as shelf-stable milk atordinary temperatures (UHT milk), yoghurts, fresh creams, sour creams,cheeses, and the like. The lactase preparation is used by a method andin usage (with the proviso that the amount is calculated based on itslactase activity) that are common in this technical field.

EXAMPLES

Below, the present invention will be specifically explained by referringto Examples.

Example 1 Development of Method for Determining Arylsulfatase Activity(Part 1)

GODO-YNL2 (liquid lactase preparation, produced by Godo Shusei Co. Ltd.)was subjected to 5-fold dilution with 100 mM potassium phosphate buffer(pH 6.5) containing 0, 0.2, 0.5, or 1.0M potassium chloride. To 0.5 mLof each solution, 0.5 mL of p-nitrophenyl sulfate in 100 mM potassiumphosphate buffer (pH 6.5) was added and the solution was allowed toreact at 37 degrees Celsius for 3 hours. The reaction was stopped byadding to the solution 1.5 mL of 1.5N aqueous sodium hydroxide solutionand the absorbance was determined at 410 nm. Relative values are shownin Table 1, in which the case where there is no potassium chloride isspecified as 100%.

TABLE 1 Increase of Determined Value of Arylsulfatase Activity byPotassium Chloride Concentration of Potassium Chloride in ReactionSystem (M) 0 0.1 0.25 0.5 Relative Value (%) 100 230 350 420

As shown in Table 1, the determined values of arylsulfatase activityincreased by the addition of potassium chloride. In other words, by theaddition of potassium chloride, a higher sensitive assay was able to beattained.

Example 2 Development of Method for Determining Arylsulfatase Activity(Part 2)

(1) GODO-YNL2 (liquid lactase preparation, produced by Godo Shusei Co.Ltd.) was subjected to 100-fold dilution with 100 mM potassium phosphatebuffer (pH 6.5) containing 0, 125, 250, 500, or 1,000 mM sodiumchloride. To 0.5 mL of each solution, 0.5 mL of 2 mM aqueous potassium4-methylumbelliferone sulfate solution was added and the solution wasallowed to react at 37 degrees Celsius for 3 hours. The reaction wasstopped by adding to the solution 1.0 mL of 0.1N aqueous sodiumhydroxide solution and the fluorescence intensity was determined at anexcitation wavelength of 360 nm and a fluorescence wavelength of 450 nm.Relative values are shown in Table 2, in which the case where there isno sodium chloride is specified as 100%.

(2) The reaction and determination of fluorescence were performed in thesame way as those described in the above (1), except that 100 mM sodiumphosphate buffer (pH 6.5) was used as the diluent for the enzyme insteadof 100 mM potassium phosphate buffer (pH 6.5). The results are shown inTable 2.

(3) The reaction and determination of fluorescence were performed in thesame way as those described in the above (1), except that potassiumchloride was added to the diluent for the enzyme instead of sodiumchloride. The results are shown in Table 2.

(4) The reaction and determination of fluorescence were performed in thesame way as those described in the above (1), except that 100 mM sodiumphosphate buffer (pH 6.5) was used instead of 100 mM potassium phosphatebuffer (pH6.5) as the diluent for the enzyme, and that potassiumchloride was added to the diluent for the enzyme instead of sodiumchloride. The results are shown in Table 2.

TABLE 2 Increase of Determined Value of Arylsulfatase Activity byCombination of Inorganic Salt and Buffer Type of Relative Value (%)Buffer and Concentration of Inorganic Salt Concentration in Type ofInorganic in Reaction System (mM) Reaction System Salt 0 62.5 125 250500 50 mM Potassium Sodium Chloride 100 230 310 440 600 Phosphate Buffer50 mM Sodium Sodium Chloride 100 200 310 410 550 Phosphate Buffer 50 mMPotassium Potassium 100 230 330 460 640 Phosphate Buffer Chloride 50 mMSodium Potassium 100 220 340 470 600 Phosphate Buffer Chloride

As shown in Table 2, the determined values of arylsulfatase activityincreased at an approximately similar rate when sodium chloride orpotassium chloride was added as an inorganic salt, and the reaction anddetermination were performed in potassium phosphate or sodium phosphatebuffer.

Example 3 Development of Method for Determining Arylsulfatase Activity(Part 3)

(1) GODO-YNL2 (liquid lactase preparation, produced by Godo Shusei Co.Ltd.) was subjected to 100-fold dilution with 100 mM, 125 mM, 250 mM,500 mM, or 1,000 mM potassium phosphate buffer (pH 6.5). To 0.5 mL ofeach solution, 0.5 mL of 2 mM aqueous potassium 4-methylumbelliferonesulfate solution was added and the solution was allowed to react at 37degrees Celsius for 3 hours. To the solution, 1.0 mL of 0.1N aqueoussodium hydroxide solution (for 100 mM, 125 mM, and 250 mM potassiumphosphate buffers) or 1.0N aqueous sodium hydrochloride solution (for500 mM and 1,000 mM potassium phosphate buffers) was added to stop thereaction, and the fluorescence intensity was determined at an excitationwavelength of 360 nm and a fluorescence wavelength of 450 nm. Relativevalues are shown in Table 3, in which the case where 100 mM potassiumphosphate buffer was used is specified as 100%.

(2) The reaction was performed in the same way as that described in theabove (1), except that the enzyme was diluted with 100 mM potassiumphosphate buffer (pH 6.5) and 0, 125, 250, 500, or 1,000 mM ammoniumsulfate was added. For the system to which 1,000 mM ammonium sulfate hadbeen added, 1.0 mL of 1.0N aqueous sodium hydroxide solution was addedto stop the reaction, and for other systems, 1.0 mL of 0.1N aqueoussodium hydroxide solution was added to stop the reaction. Thefluorescence intensity was determined at an excitation wavelength of 360nm and a fluorescence wavelength of 450 nm. Relative values are shown inTable 4, in which the determined value of activity of the systemcomprising no ammonium sulfate added is specified as 100%.

(3) The reaction and. determination of fluorescence were performed inthe same way as those described in the above (2), except that 0, 125,250, 500, or 1,000 mM glucose was added to the diluent of the enzymeinstead of ammonium sulfate. The results are shown in Table 4.

TABLE 3 Increase of Determined Value of Arylsulfatase Activity byPotassium Phosphate Buffer Concentration of Potassium Phosphate Bufferin Reaction System (mM) 50 62.5 125 250 500 Relative Value (%) 100 140190 160 170

TABLE 4 Increase of Determined Value of Arylsulfatase Activity byCombination of Additive and Buffer Relative Value (%) Type of Buffer andIts Concentration of Additive Concentration in Type of in ReactionSystem (mM) Reaction System Additive 0 62.5 125 250 500 50 mM PotassiumAmmonium 100 270 370 390 400 Phosphate Buffer Sulfate 50 mM PotassiumGlucose 100 140 190 160 170 Phosphate Buffer

As shown in Table 3, although the increase in buffer concentration alsocontributed to rise of determined values of arylsulfatase activity, theeffect was small. Further, as shown in Table 4, the addition of ammoniumsulfate increased the determined values of arylsulfatase activity,whereas glucose showed a minor effect to increase the determined valuesof arylsulfatase activity.

Example 4 Confirmation of Step in Which Effect of Addition of InorganicSalt is Arisen

It was confirmed that the effect of addition of an inorganic salt is dueto promoted enzyme reaction or enhanced fluorescence intensity offluorophore.

GODO-YNL2 (liquid lactase preparation, produced by Godo Shusei Co. Ltd.)was subjected to 100-fold dilution with 100 mM potassium phosphatebuffer (pH 6.5). Further, it was separately subjected to 100-folddilution with 100 mM potassium phosphate buffer (pH 6.5) containing 0.5Mpotassium chloride. To 0.5 mL of each solution, 0.5 mL of 2 mM aqueouspotassium 4-metylumbeliferone sulfate solution was added and thesolution was allowed to react at 37 degrees Celsius for 1 hour. To thesolution, 1.0 mL of 0.1N aqueous sodium hydroxide solution was added tostop the reaction. To 200 μL of each solution after stopping thereaction, 200 μL of an aqueous solution containing potassium chloride ata concentration of 0 mM, 125 mM, 250 mM, 500 mM, or 1,000 mM was added,and the fluorescence intensity was determined at an excitationwavelength of 360 mm and a fluorescence wavelength of 450 nm. As ablank, a solution was used, which solution had been prepared by adding0.1N aqueous sodium hydroxide solution to a diluted enzyme solution toinactivate and then adding aqueous potassium 4-metylumbelliferon sulfatesolution.

Relative values are shown in Table 5, in which the case where thelactase preparation that had been subjected to 100-fold dilution with100 mM potassium phosphate buffer (pH 6.5) was used for the reaction andpotassium chloride was not added after stopping the reaction (200 μL ofdistilled water with potassium chloride concentration of 0 mM was added)is specified as 100%.

TABLE 5 Confirmation of Step in which Effect by Addition of InorganicSalt Is Shown Relative Value (%) Concentration of Potassium Chloride(mM) in Aqueous Potassium Chloride Solution That Was Added afterStopping Reaction Condition during Reaction 0 125 250 500 1000 In Casewhere Reaction 100 100 100 100 100 Was Performed in (basis) 50 mMPotassium Phosphate Buffer (%) In Case where Reaction 520 520 520 510490 Was Performed in 50 mM Potassium Phosphate Buffer + 250 mM PotassiumChloride (%)

As shown in Table 5, when the inorganic salt had been added beforestarting the reaction, i.e., when the enzyme reaction was performed inthe presence of the inorganic salt, the fluorescence intensity wasenhanced, whereas the fluorescence intensity was not enhanced, when theinorganic salt was added after the completion of the enzyme reaction.Accordingly, it became clear that because the inorganic salt promotedthe enzyme reaction to increase the absolute amount of the fluorophoreliberated, the fluorescence intensity was enhanced.

Example 5 Determination of Arylsulfatase Activity by ConventionalColorimetric Method

GODO-YNL2 (liquid lactase preparation, produced by Godo Shusei Co. Ltd.)was diluted with distilled water to obtain a 1% (w/v) solution. Thesolution was diluted with 100 nM potassium phosphate buffer (pH 6.5)containing 0.5M potassium chloride to obtain 0.8% (w/v), 0.6% (w/v),0.4% (w/v), and 0.2% (w/v) solutions. To 0.5 mL of each solution, 0.5 mLof 100 mM potassium phosphate buffer (pH 6.5) containing 20 mMp-nitrophenyl sulfate was added and the solution was allowed to react at37 degrees Celsius for 3 hours. The reaction was stopped by adding tothis solution 1.5 mL of 1.5N aqueous sodium hydroxide solution, and theabsorbance was determined at 410 nm.

The results are shown in FIG. 1. By the colorimetric method, noarylsulfatase activity was detected for the 1% (w/v) solution of theenzyme preparation.

Example 6 Determination of Arylsulfatase Activity by Fluorescence Method

GODO-YNL2 (liquid lactase preparation, produced by Godo Shusei Co. Ltd.)was diluted with 100 mM potassium phosphate buffer (pH 6.5) containing0.5M potassium chloride to obtain a 1% (w/v) solution. This 1% solutionwas further diluted with the same buffer to obtain 0.8% (w/v), 0.6%(w/v), 0.4% (w/v), and 0.2% (w/v) solutions.

To 0.5 mL of each solution, 0.5 mL of 2 mM aqueous potassium4-methylumbelliferyl sulfate solution was added and the solution wasallowed to react at 37 degrees Celsius for 3 hours. To this solution,1.0 mL of 0.1N aqueous sodium hydroxide solution was added to stop thereaction, and the fluorescence intensity was determined at an excitationwavelength of 360 nm and a fluorescence wavelength of 450 nm.

The results are shown in FIG. 2. By the fluorescence method, unlike thecolorimetric method, the solutions of the enzyme preparation having itsconcentration of 1% (w/v) or lower also showed good quantitativeperformance.

Example 7 Comparison of Colorimetric and Fluorescence Methods inarylsulfatase activity determination

The difference between sensitivities of colorimetric and fluorescencemethods in the determination of arylsulfatase activity was studied.First, purified lactase for use in this experiment was prepared.

Preparation of Purified Lactase

To 50 kg of GODO-YNL2 (liquid lactase preparation, produced by GodoShusei Co. Ltd.), water was added to desalt by using an ultrafiltrationmembrane (ACP membrane, produced by Asahi Kasei Corp.) until theconductivity became 3 mSv or lower. The total amount was adjusted to 125L by adding water. Then, it was adsorbed to ion exchange resin (DEAETOYOPEABL 650M, 40 cmφ, 50 L, produced by Tosoh Corp.) pre-equilibratedwith 10 mM potassium phosphate buffer (pH 7). The resin was washed with40 L of 10 mM potassium phosphate buffer (pH 7) containing 50 mM sodiumchloride, and then lactase was eluted with 200 L of 10 mM potassiumphosphate buffer (pH 7) containing 100 mM sodium chloride. Upon elution,the eluate was divided into 20 L fractions. The lactase activity (by theFCC IV method; Food Chemicals Codex 4th Edition, Effective Jul. 1, 1996,Committee on Food Chemicals Codex, p.p. 801-802) and arylsulfataseactivity (by the fluorescence method; it will be described below indetail) of each fraction were determined, and fractions with reducedarylsulfatase were collected, mixed, and concentrated using anultrafiltration membrane (ACP membrane, produced by Asahi Kasei Corp.)to obtain a concentrated lactase solution. To this concentratedsolution, glycerol was added to be 50% (w/v). Thus, a purified lactasepreparation was obtained.

Arylsulfatase activity of GODO-YNL2 (liquid lactase preparation,produced by Godo Shusei Co. Ltd.) and the purified lactase preparationprepared as described above, both of which had lactase activity by theFCC IV method of 5,000 to 6,500 NLU/g, were determined (the fluorescencemethod; it will be described below in detail). The arylsulfataseactivity of purified lactase preparation was determined as being 1/840as compared to that of pre-purification (see Table 6 below).

Preparation of Enzyme Preparations with Various Contamination Rates ofArylsulfatase

The purified lactase preparation prepared as described above andGODO-YNL2 (liquid lactase preparation, produced by Godo Shusei Co. Ltd.)were appropriately mixed to prepare lactase preparations with variouscontamination rates of arylsulfatase, and the lactase activity (by theFCC IV method) and the arylsulfatase activity (by the colorimetric andfluorescence methods) were determined.

Determination of Arylsulfatase Activity by Colorimetric Method

To 0.5 mL of the lactase preparation, 0.5 mL of 100 mM potassiumphosphate buffer (pH 6.5) containing 20 mM p-nitrophenyl sulfate wasadded and the solution was allowed to react at 37 degrees Celsius for 3hours. To this solution, 1.5 mL of 1.5N aqueous sodium hydroxidesolution was added to stop the reaction, and the absorbance wasdetermined at 410 nm.

Separately, aqueous solutions containing p-nitrophenol at aconcentration of 0 to 0.5 mM were prepared. To 0.5 mL of each solution,0.5 mL of 100 mM potassium phosphate buffer (pH 6.5) was added. Further,1.5 mL of 1.5N aqueous sodium hydroxide solution was added to obtainsamples for determination. The absorbance at 410 nm was determined toprepare a calibration curve.

From the calibration curve, the concentration of p-nitrophenol containedin 1 mL of the reaction solution was determined, and divided by 3(because the reaction time was 3 hours), to calculate the p-nitrophenolconcentration for the reaction time of period of 1 hour. Then, from thisconcentration, the amount of p-nitrophenol contained in 1 mL of thereaction solution (unit: nmole) was calculated, and multiplied by 2 (forconverting the value into per 1 g, because the amount of lactasepreparation used was 0.5 g), to calculate the arylsulfatase activity.One U corresponds to the activity which produces 1 nmole ofp-nitrophenol in 1 hour, and the arylsulfatase activity is representedby the unit “U/g-enzyme preparation.”

Determination of Arylsulfatase Activity by Fluorescence Method

The lactase preparation was diluted with 100 mM potassium phosphatebuffer (pH 6.5) containing 0.5M potassium. chloride to obtain a 1% (w/v)solution. To 0.5 mL of this 1% solution, 0.5 mL of 2 mM aqueouspotassium 4-methylunbelliferyl sulfate solution was added and thesolution was allowed to react at 37 degrees Celsius for 3 hours. To thesolution 1 mL of 0.1N aqueous sodium hydroxide solution was added tostop the reaction, and the fluorescence intensity was determined at anexcitation wavelength of 360 nm and a fluorescence wavelength of 450 nm.

Separately, 100 mM potassium phosphate buffers (pH 6.5) containing 0.5Mpotassium chloride and 4-methylumbelliferone at a concentration of 0 to4 μM were prepared. To 1.0 mL of each solution, 1 mL of 0.1N aqueoussodium hydroxide solution was added to obtain samples for determination.The fluorescence intensity was determined at an excitation wavelength of360 nm and a fluorescence wavelength of 450 nm to prepare a calibrationcurve.

From the calibration curve, the concentration of 4-methylumbelliferonecontained in 1 mL of the reaction solution was determined and it wasdivided by 3 (because the reaction time of period was 3 hours). Then,from the volume of the reaction solution, the absolute amount of4-methylumbelliferone produced during the reaction was calculated. Theamount was further multiplied by 200 (for converting the value into per1 g of the specimen (lactase preparation), because the amount of lactasepreparation used was 0.5×0.01=0.005 g), and thereby arylsulfataseactivity was calculated. One U is such an activity that 1 nmole of4-methylumbelliferone is produced in 1 hour, and the arylsulfataseactivity is represented by the unit “U/g-enzyme preparation.”

Results

The results are shown in Table 6. By the colorimetric method,determination was not possible when the content of arylsulfatasedecreased, whereas by the fluorescence method it was possible toaccurately determine until the concentration area of about 1/100 of thedetection limit by the colorimetric method.

TABLE 6 Lactase Activity and Arylsulfatase Activity of LactasePreparations Containing Arylsulfatase in Various Contamination RatesArylsulfatase Arylsulfatase Activity (U/g) Activity of Conven- MethodThis Lactase tional of Invention/ Activity Colorimetric This Lactase(NLU/g) Method Invention Activity (%) GODO-YNL2 5400 39 84 1.56 Mixtureof (5500) 8.7 20 0.36 GODO-YNL2 (5400) ND 15 0.28 with Purified Lactase(5300) ND 1 0.02 Purified Lactase 5500 ND 0.1 0.002 ND: Not Detected

Example 8 Comparison of Fluorescence Method and the Method as Stated inWO07/060247 (Japanese Patent Laid-Open No. 2009-517061) in Determinationof Arylsulfatase Activity, and Organoleptic Examination for Taste (Part1)

In WO07/060247, it is described that a lactase preparation contaminatedwith 19 units (units that are defined in WO07/060247) or less ofarylsulfatase does not produce off-flavor when the preparation is addedto decompose lactose after sterilization of milk. However, this is anobservation based on an examination that was performed with the limitedlactase reaction time of period of 2 days. On the other hand, when alactase preparation is actually added to shelf-stable milk at ordinarytemperatures (UHT milk), it is thought that enzyme reaction wouldproceed for a long term of 1 month or more. Therefore, lactasepreparations containing arylsulfatase at various contaminating rateswere prepared and their taste was confirmed after predetermined daysfrom the addition of the preparations to milk.

Preparation of Lactase Preparations with Various Contamination Rates ofArylsulfatase

Lactase preparations A to E having various contamination rates ofarylsulfatase were produced by appropriately mixing the purified lactasepreparation prepared in Example 7 and selected GODO-YNL2 (liquid lactasepreparation, produced by Godo Shusei Co. Ltd.) containing 100 units(based on that described in WO07/060247) of arylsulfatase activity.

The arylsulfatase activity of each of thus prepared lactase preparationsA to E was determined by the method described in WO07/060247 and thefluorescence method shown in Example 7 above. Further, the lactaseactivity was determined by the FCC IV method. The results are shown inTable 7. In this Table, the unit as described in WO07/060247 meansΔOD₄₁₀×1⁶/hour/NLU.

TABLE 7 Arylsufatase Activity in Lactase Preparations ContainingArylsulfatase in Various Contamination Rates Arylsulfatase Activity(unit) that Was Determined by Arylsulfatase Name of the Method ActivityLactase Described in Arylsulfatase of This Preparation WO07/060247Activity (U/g) that Invention/ and Lactase (Japanese Patent WasDetermined Lactase Activity Laid-open No. by the Method of Activity(NLU/g) 2009-517061) Present Invention (%) A (5500) ND 0.1 0.002 B(5500) ND 1.0 0.02 C (5500) 8 27 0.5 D (5500) 18 59 1.1 E (5500) 100 3205.8 ND: Not Detected

Organoleptic Examination of Taste

Referring to Example 4 of WO07/060247, each of the lactase preparationsA to E was added to a commercially available cow milk (heat-sterilizedone; sterile conditions: 130 degrees Celsius, 2 seconds) so that thelactase content would become 20,000 NLU/L-milk, and was kept at 30degrees Celsius. After 2 days, 1 month, and 3 months of storage, anorganoleptic examination was performed for the cow milk to which nolactase preparation had been added mid the milks to which lactasepreparations had been added.

The organoleptic examination was performed as a blind study. Eleven tothirteen panelists smelled and held in mouth the milk after storage fora certain period of time to judge the presence or absence of off-flavor.The evaluation was performed by scoring 0 point (−) for no off-flavor, 1point (+) which meant that the panelist was aware of off-flavor, or 2points (+) which meant that the panelist was strongly aware ofoff-flavor. The results are summarized in Table 8.

TABLE 8 Results of Organoleptic Examination of Taste (Off-flavor) of CowMilks that Were Treated by Lactase Preparations Containing Arylsulfatasein Various Contamination Rates Lactase Reaction Time of PeriodPreparations 2 days 1 month 3 months Not Added − − − A − − − B − − − C −++ ++ D − ++ ++ E + ++ ++ ++: Strongly Aware +: Aware −: Not Aware

After 2 days of the reaction time of period by the lactase preparation(i.e., storage time of period of cow milk), only preparation E exhibitedapparent off-flavor. This was coincided with the description inWO07/060247. However, when the reaction time of period was 1 month orlonger, preparations C and D also exhibited noticeable off-flavor. Thisindicates that unusual taste and off-flavor cannot be sufficientlycontrolled even though the arylsulfatase activity is 8 units, which isthe detection limit in the unit described in WO07/060247, consideringthat the lactase preparations is used in, e.g., shelf-stable milk atordinary temperatures (UHT milk).

On the other hand, preparations A and B exhibited no noticeableoff-flavor for the reaction time of period of 1 and 3 months.Considering the use of the lactase preparation in shelf-stable milk atordinary temperatures (UHT milk), it is necessary to assume a reactiontime of period of 1 month or longer. Therefore, for such usage, itbecame clear that it is preferable to use lactase preparation A or B(i.e., one having a ratio of the arylsulfatase activity by the method ofpresent invention to the lactase activity by the FCC IV method of 0.02%or less) and that it is more preferable to use lactase preparation A.Further, it became clear that it is necessary to determine thearylsulfatase activity value which is comparable to that of lactasepreparation A or B by the fluorescence method as described in thisdescription or by an analysis method having a sensitivity similar to orhigher than the above fluorescence method.

Example 9 Obtaining a Mutant having a Reduced ArylsulfataseProducibility

A loopful of Kluyveromyces lactis G14-427, which was a diploid strain,was inoculated into 10 ml of YPD medium (containing 1% of yeast extract,1% of glucose, and 2% of peptone). The obtained suspension of cells wasstored at 30 degrees Celsius to cultivate the cells. After arriving at alogarithmic phase, the suspension was centrifuged and then the cellswere gathered. The gathered cells were dispersed in sterile water sothat the absorbance of the obtained suspension would become 0.5 at 600nm. By using a UV lamp, ultraviolet was irradiated to the suspension for15 seconds. The cells were gathered by centrifugation, and then thegathered cells were dispersed in YPD medium by mixing. From the YPDmedium comprising the cells, an optimal dose of the YPD medium was takenand applied onto a YPD agar plate. Static culture of the plate wasperformed at 37 degrees Celsius for 7 days. From a colony that had growna small amount of cells were scratched, and then the scratched cellswere mixed with 1 ml of a solution comprising Zymolyase (produced bySeikagaku Bio-business Corporation) in an amount of 1 mg/mL. Reactionwas performed at 30 degrees Celsius for 2 hours to destroy cell walls.Thereafter centrifugation was performed and supernatant was gathered.

Lactase activity (the FCC IV method) and arylsulfatase activity (by thefluorescence method disclosed in Example 7) of the supernatant weredetermined. The ratio of the arylsulfatase activity to the lactaseactivity was calculated and strains that exhibit small values wereselected.

Selected strains were repeatedly subjected to the above treatments formutation and selection. As a result, a mutant (SM1182 strain) was ableto be obtained, in which strain one arylsulfatase gene among twoarylsulfatase genes that had existed in the diploid strain,Kluyveromyces lactis G14-427, became dysfunctional. The judgment that“one arylsulfatase gene among two arylsulfatase genes becamedysfunctional” was based on the following fact: the culture supernatantof SM1182 strain exhibited an arylsulfatase activity of about one-halfof that of the culture supernatant of the mother strain, G14-427 strain.

Furthermore, the obtained mutant (SM1182 strain) was used as a motherstrain and treatments to cause mutation were performed. As a result, amutant (SF-81 strain) in which the other arylsulfatase gene had alsobecome dysfunctional, namely, one having an arylsulfatase activity ofzero, was obtained.

Kluyveromyces lactis G14-427 as a mother strain and two mutants that hadbeen obtained by the methods described above were respectivelycultivated by shaking in YPD medium (70 mL/flask) at 26 degrees Celsiusfor 4 days.

Thereafter, to each culture medium Zymolyase (produced by SeikagakuBio-business Corporation) was added to be a concentration of 2 mg/mL.Reaction was performed at 30 degrees Celsius for 2 hours to destroy cellwalls. Supernatants were respectively gathered by centrifugation, andwere subjected to determinations of the lactase activity by the FCC IVmethod and the arylsulfatase activity by the method disclosed in Example7. Table 9 shows the result.

TABLE 9 Comparison of Arylsulfatase Activity of Parent Strain and MutantStrain Lactase Arylsulfatase Activity (NLU/g) Activity (U/g) G14-427Strain 16 6 SM1182 Strain 16 3 SF-81 Strain 16 0

Example 10 Obtaining Host Strain

To 10 mL of YPD medium, a loopful of Kluyveromyces lactis G14-427strain, which was a diploid strain, was inoculated, and the cells weregrown to log phase at 30 degrees Celsius. The cells were gathered bycentrifuging the culture medium. The gathered cells were dispersed insterile water so that the absorbance of the obtained suspension wouldbecome 0.5 at 600 nm. By using a UV lamp, ultraviolet was irradiated tothe cell suspension for 15 seconds. The cells were gathered bycentrifugation, and mixed and dispersed in YPD medium. An appropriateamount of YPD medium containing the cells was taken and was spread on aYPD agar plate. Static culture of the plate was performed at 37 degreesCelsius for 4 days under static conditions. The colonies that had grownwere cultured on SD medium (0.67% amino acid-free yeast nitrogen base,2% glucose, 2% agar) after their replica-plating, and those that had notbe able to grow were selected.

These strains that had not be able to grow on the above SD medium werespread on another SD medium containing 20 mg/L of L-methionine from theoriginal YPD agar plate, and those that had grown were designated asL-methionine-requiring mutant (7-19 strain).

To 10 mL of YPD medium, a loopful of the 7-19 strain was inoculated, andthe cells were grown to log phase at 30 degrees Celsius. The cells weregathered by centrifuging the culture medium. The gathered cells weredispersed in sterile water so that the absorbance of the obtainedsuspension would become 0.5 at 600 nm. By using a UV lamp, ultravioletwas irradiated to the cell suspension for 15 seconds. The cells weregathered by centrifugation, and mixed and dispersed in YPD medium. Anappropriate amount of YPD medium containing the cells was taken and wasspread on a YPD agar plate. Static culture of the plate was performed at37 degrees Celsius for 4 days. The colonies that had grown were culturedon SD medium containing 20 mg/L of L-methionine after theirreplica-plating, and those that had not be able to grow were selected.

These strains that had not be able to grow on the above SD mediumcontaining L-methionine were spread on another SD medium containing 20mg/L of L-histidine and 20 mg/L of L-methionine from the original YPDagar plate, and those that had grown were designated as L-methionine andL-histidine double nutrient-requiring mutant (8-23 strain). The growthof nutrient-requiting mutants obtained is shown in Table 10.

TABLE 10 Growth of Mutant Strains in Various Culture Media SD Medium +SD SD Medium + L-Methionine + Medium L-Methionine L-Histidine G14-427Strain + + + 7-19 Strain − + + 8-23 Strain − − + +: Grew −: Not Grew

Example 11 Obtaining Gene Double-Disrupted Strain which does not ProduceArylsulfatase Obtaining Host Strain

It was confirmed that in the 8-23 strain that was the L-histidine andL-methionine double nutrient-requiring mutant obtained in Example 10,the nutrient requirements would be complemented by HIS4 gene and MET6gene, respectively, introduced by the lithium acetate method.

Obtaining Genomic DNA

Kluyveromyces lactis G14-427 strain, which was a diploid strain, wascultured in YPD medium. From the culture fluid obtained, genomic DNA wasprepared using Dr. Gen'TLE™ (from yeast) (produced by Takara Bio Inc.).The manipulation was performed according to the instructions in theoperating manual attached to Dr. GenTLE™ (from yeast).

Construction of Vector for Disrupting Arylsulfatase Gene

Primers SuC-F and Sue-R were designed so that a fragment containing theopen reading frame of arylsulfatase gene would be obtained. Thesequences of used primers including them were as shown in Table 11.

TABLE 11  Used Primer Name of Primer Sequence (5′→3′) SuC-FATGACCAAAACAGATGAACCTA SuC-R CCAGTCTCTTGCGTCGTGA BGLHIS4-FGAAGATCTCAGACCTGAGGTAACGTTTC HIS4-R CTGGGTAACTTGTTCTGGTG SuCd-M6FATCGATGTTGTTGAGCGGTACTGACAACCAT-- TTGGCAGGTTTCATCAACACACGAGCCG SuCd-M6RATCGATAACTCTACCGATATTTTGGTCTAATT-- CATCAACCACTGTTGGTGGAG

A DNA fragment was obtained by performing PCR under the followingconditions with the genomic DNA prepared in advance as the template byusing the above primers. As the polymerase, Takara Ex Taq (registeredtrademark; produced by Takara Bio Inc.) was used and the manipulationwas performed according to the attached instructions.

PCR Conditions

Stage 1 (1 cycle) 94 degrees Celsius, 3 min.

Stage 2 (30 cycles) 94 degrees Celsius, 1 min.

-   -   54 degrees Celsius, 1 min.    -   72 degrees Celsius, 3 min.

Stage 3 (1 cycle) 72 degrees Celsius, 10 min.

-   -   Kept at 4 degrees Celsius

The obtained fragment was purified by MagExtractor™—PCR & Gel Cleanup—(produced by Toyobo Co., Ltd.), and then a ligation reaction of thefragment with pGEM (registered trademark)—T vector (produced by Promega)was performed. For the ligation reaction, DNA Ligation Kit <Mighty Mix>(produced by Takara Bio Inc.) was used. The methods of using were asstated in respective attached documents. Then, competent cells of E.coli DH5α strain that had been prepared according to the Hanahan method(Hanahan, D., J. Mol. Biol., 166, 557 (1983)) were transformed, and fromthe culture fluid of the obtained transformant, plasmid was extracted byusing MagExtractor™—Plasmid (produced by Toyobo Co., Ltd.). The methodof using was as stated in the attached document. As a result, plasmidpGSuC, in which the intended fragment had been subcloned, was obtained.

Further, by performing PCR using primers BGLHIS4-F and HIS4-R withgenomic DNA as the template, a fragment containing HIS4 gene wasobtained. PCR was performed as the method described above. As shown inFIG. 3, the obtained fragment containing HIS4 gene was treated with BglII and Eco RI and then it was inserted into the Bgl II-EcoRI site ofpGSuC. The thus constructed plasmid was designated as pdSuC1. Thevarious methods used for construction were similar to those statedabove.

To construct a vector for disrupting arylsulfatase gene with MET6 geneas a marker, primers SuCd-M6F and Sued-MGR each having 40 bases ofhomologous sequence of arylsulfatase gene added to the 5′-side weredesigned. The homologous sequences of arylsulfatase gene were near therestriction enzyme sites for Cla I, which existed two locations in theopen reading frame. As shown in FIG. 4, a fragment having homologoussequences to arylsulfatase at the both ends of MET6 gene was obtained byusing these primers and genomic DNA as the template. The obtainedfragment was subcloned into pGEM (registered trademark)—T vector(produced by Promega) to obtain pdSuCM6. The various methods used forconstruction were similar to those stated above.

Transformation of L-Methionine and L-Histidine Double Nutrient-RequiringMutant 8-23 Strain by Using a Vector for Disrupting Arylsulfatase Gene

FIG. 5 represents a schematic diagram of construction of a transformant.Plasmid pdSuC1 was linearized by treating with Nco I and Aat II,followed by transformation of the 8-23 strain with the linearizedplasmid by the lithium acetate method. Thus, a transformant, SuCDstrain, was obtained, which strain grew on SD medium with 20 μg/mL ofmethionine added.

Then, plasmid pdSuCM6 was linearized by treating with Cla I, followed bytransformation of the SuCD strain with the linearized plasmid by thelithium acetate method. Thus, a transformant, SuCDD5-2 strain, wasobtained, which strain grew on SD medium.

Southern Blotting of DNAs from Parent Strain and Transformant Strains

Obtained transformants were respectively cultured in YPD medium, andgenomic DNAs were respectively prepared from the culture fluids usingDr. GenTLE™ (from yeast) (produced by Takara Bio Inc.). The obtainedgenomic DNAs were digested with Barn HI, followed by Southern analyses.As the probe, the Aat II-Eco RI fragment of arylsulfatase gene was used.For labeling and detection of nucleic acid, AlkPhos Direct Labeling andDetection System with CDP-Star (produced by GE Healthcare BioscienceCo., Ltd.) was used, and the method of using was according to theattached document.

The results of Southern blotting are shown in FIG. 6. Lanes 1, 2, and 3represent the parent strain G14-427, the transformant SuCDD5-2, and thetransformant SuCD, respectively. In lane 3, with the band (12.1 kb) offragment containing arylsulfatase gene and HIS4 gene, a band at the sameposition (7.8 kb) in lane 1 was also detected. Thus, it was confirmedthat only one of the arylsulfatase genes had been disrupted. On theother hand, in lane 2, the band of 7.8 kb shifted to 5.3 kb. Thus, itwas confirmed that both arylsulfatase genes had been disrupted.

Detection of Arylsulfatase Activity in Arylsulfatase Gene-DoubleDisrupted Strain

The parent strain, Kluyveromyces lactis G14-427 strain (a diploidstrain) and the SuCDD5-2 strain constructed as described above wererespectively inoculated to YPD medium, and incubated at 30 degreesCelsius, with shaking at 210 rpm for 72 hours. To each culture fluid,Zymoliase (produced by Seiltagaku Biobusiness Corp.) was added to be aconcentration of 2 mg/mL, and reaction was performed at 30 degreesCelsius for 2 hours to disrupt the cell walls. Supernatants wererespectively gathered by centrifugation, and the lactase activity andarylsulfatase activity were determined by the FCC IV method and themethod as described in Example 7, respectively. The results are shown inTable 12.

It has been revealed that although in the culture fluid of the SuCDD5-2strain, lactase is contained, arylsulfatase is not contained or iscontained in a very small amount if any such that it cannot be detectedby the fluorescence method. Namely, it has been confirmed that althoughthe SuCDD5-2 strain maintains the productivity of lactase, productivityof arylsulfatase is zero or almost zero.

TABLE 12 Comparison between Arylsulfatase Activity of Strain having TwoArylsulfatase Genes and Other Strain in Which Both Arylsulfatase GenesHad Been Disrupted Strain that Lactase Arylsulfatase Produces LactaseActivity (NLU/g) Activity (U/g) G14-427 Strain 16 6 SucDD5-2 Strain 16 0

Example 12 Preparation of Enzyme Preparations with SF-81 Strain andCBS2359 Strain

The SF-81 strain (a diploid mutant with reduced arylsulfataseproductivity) obtained in Example 9 and CBS2359 strain (a monoploidstrain) were respectively inoculated to a medium for lactase productioncontaining 7% corn steep liquor and 2% lactose, and incubated at 30degrees Celsius with shaking at 210 rpm for 96 hours. Then, the cellswere respectively gathered by centrifugation. Sterile purified water wasadded to the cells and the cell walls of the gathered cells weredisrupted with glass beads and ultrasonic waves. The thus obtainedmixture containing cells, purified water, and the like, was centrifugedand supernatant was gathered. The lactase activity of the obtainedsupernatant was determined by the fluorescence method as described inExample 7. As a result, the relative activity of the CBS2359 strain was2% as compared to the lactase activity of the SF-81 strain that wasspecified as 100%.

The above supernatant was fractionated with ammonium sulfate andconcentrated with an ultrafiltration membrane. As a result, from cellsof the SF-81 strain, lactase preparations were obtained, whichpreparations have respective lactase activity of about 1,000, 2,000,3,000, 4,000, 5,000, or 6,000 NLU/g depending on the degree ofconcentration. On the other hand, no preparation was obtained havinglactase activity of 1,000 NLU/g or higher from the CBS2359 strainalthough a similar concentration method was performed.

Example 13 Preparation of Enzyme Preparation

The SF-81 strain was inoculated to a medium for lactase productioncontaining 7% corn steep liquor and 2% lactose, and incubated at 30degrees Celsius with shaking at 210 rpm for 96 hours. Then, the cellswere gathered by centrifugation. Sterile purified water was added to thecells and the cell walls of the gathered cells were disrupted with glassbeads and ultrasonic waves. The supernatant was gathered bycentrifugation. The supernatant was fractionated with ammonium sulfateand concentrated by an ultrafiltration membrane to obtain a lactasepreparation having lactase activity of about 5,000 NLU/g. Thearylsulfatase activity of this lactase preparation was 1 U/g or lessaccording to the method of the present invention (the fluorescencemethod).

Example 14 Organoleptic Examination for Taste (Part 2) Preparation ofLactase Preparations with Various Contamination Rates of Arylsulfatase

Five lactase preparations each having arylsulfatase activity of 1 to 20U/g as determined by the fluorescence method shown in Example 7 wereprepared from the lactase preparation per se produced from the SF-81strain by the method as described in Example 13, and by appropriatelymixing the lactase preparation with GODO-YNL2 (liquid lactasepreparation, produced by Godo Shusei Co. Ltd.). Further, the lactaseactivity of each lactase preparation was determined by the FCC IVmethod.

Organoleptic Examination for Taste

As is in Example 8, each of the 5 lactase preparations was added to acommercially available cow milk to be the lactase content of 20,000NLU/L-milk, and the obtained cow milks were stored at 30 degreesCelsius. After 1 month of storage, an organoleptic examination for tastewas performed by a similar method as described in Example 8, in whichthe milks to which lactase preparations had been respectively added werecompared to the milk to which lactase preparation had not been added.The results are shown in Table 13.

TABLE 13 Results of Organoleptic Examination for Taste (Off-flavor) ofCow Milks that Were Treated by Lactase Preparations ContainingArylsulfatase in Various Contamination Rates Lactase PreparationsArylsulfatase Off-flavor Activity/ Reaction Lactase ArylsulfataseLactase Time of Activity (NLU/g) Activity (U/g) Activity (%) Period: 1month Not Added − 5000 1 or less 0.02 or less − 5000 5 0.1 − 5000 100.2 + 5000 15 0.3 + 5000 20 0.4 + +: Aware −: Not Aware

From the results shown in Table 13, it has been concluded thatarylsulfatase activity as determined by the method according to thepresent invention is preferably 5 U/g or less. Further, it has beendemonstrated that the proportion of arylsulfatase activity (unit: U/g)as determined by the method according to the present invention ispreferably 0.1% or less by using the lactase activity (unit: NLU/g) bythe FCC IV method as the basis.

1-15. (canceled)
 16. A lactase preparation comprising lactase and havinga lactase activity of 4,000 NLU/g or more according to the FCC IVmethod, wherein the lactase originates from a lactase gene of yeast, andwherein the lactase preparation has an arylsulfatase activity of 0.1% orless based on the lactase activity, in which the arylsulfatase activity(unit: U/g) is determined and calculated by a method comprising: (a)obtaining a sample by diluting the lactase preparation as a specimen inwhich the existence of the arylsulfatase is predicted with 100 mMpotassium phosphate buffer (pH6.5) comprising 0.5M potassium chloride,(b) preparing an aqueous solution comprising potassium4-methylumbelliferone sulfate in a concentration of 2 mM, (c) mixing thesample and the aqueous potassium 4-methylumbelliferone sulfate solutionwith each other at a ratio of 1:1 (volume basis) to react them at 37degrees Celsius for 3 hours, (d) adding to the reacted solution, 0.1Naqueous sodium hydroxide solution having the same amount (volume basis)as that of the reacted solution to stop the reaction, thus obtaining asample for determination, (e) determining fluorescence intensity at anexcitation wavelength of 360 nm and a fluorescence wavelength of 450 nm,(f) preparing a plurality of 4-methylumbelliferone solutions withdifferent 4-methylumbelliferone concentrations in 100 mM potassiumphosphate buffer (pH6.5) comprising 0.5M potassium chloride, adding 0.1Naqueous sodium hydroxide solution to each of the plurality of4-methylumbelliferone solutions in a similar way as in (d), anddetermining fluorescence intensities of the plurality of4-methylumbelliferone solutions under the same conditions as in step(e), (g) preparing a calibration curve from (f), (h) from thefluorescence intensity determined in (e) and the calibration curveprepared in (g) calculating the concentration of 4-methylumbelliferoneof the sample for determination, and dividing the calculated value by 3,thus obtaining the concentration of the 4-methylumbelliferone in thecase where the reaction time of period is 1 hour; further from thevolume of the reacted solution, calculating the amount of the4-methylumbelliferone that was liberated by the reaction of one hour,(i) because the amount of the 4-methylumbelliferone thus calculated isbased on the amount of the specimen that was contained in the sampleprepared in (a), converting the calculated amount to that of the4-methylumbelliferone per 1 g of the specimen, and (j) defining 1unit(U) as the amount of the 4-methylumbelliferone, wherein 1 nmole ofthe 4-methylumbelliferone is liberated per 1 hour of the time of periodof the reaction of the substrate and the arylsulfatase, and showing theunit as a unit amount per 1 g of the specimen (i.e., the lactasepreparation), “unit(U)/g”.
 17. The lactase preparation according toclaim 16, wherein the lactase is prepared from yeast having a lactasegene in which expression of arylsulfatase protein is restricted, or agene recombinant microorganism that is transformed with a lactase geneof yeast in which expression of arylsulfatase protein is restricted. 18.The lactase preparation according to claim 16, wherein the arylsulfataseactivity (unit: U/g) is 0.02% or less based on the lactase activity(unit: NLU/g).
 19. The lactase preparation according to claim 17,wherein the yeast is a mutant that is obtained by treating yeast havinga lactase gene to mutate it.
 20. The lactase preparation according toclaim 17, wherein the yeast is a mutant that is obtained by manipulatingyeast having a lactase gene to delete an arylsulfatase gene or a gene toregulate expression of an arylsulfatase protein.
 21. The lactasepreparation according to claim 17, wherein the yeast having a lactasegene in which expression of arylsulfatase protein is restricted is adiploid strain.
 22. The lactase preparation according to claim 17,wherein the yeast having a lactase gene in which expression ofarylsulfatase protein is restricted belongs to Kluyveromyces lactis orKluyveromyces marxianus